1. Field of the Invention
The present invention relates to an interface device between a public telephone and an external terminal.
2. Description of Related Art
Portable telecommunications terminals, such as microcomputers with a communication card, are becoming evermore widely used. Their owners wish to be able to use them everywhere and, in particular, in public telephones or Publiphones (registered trademark), which are telephones using prepayment or postpayment available to the public.
In order to permit such a use, the public telephones must be equipped with an external connector. In the past, few options have been offered to users as a result of the fraud risks involved with such a connector. There has been no significant development up to now with regards to connectors for connecting external terminals, essentially for security reasons.
Reference can be made to the following solutions:
dedicated interface between a public phone and a terminal with mechanical protection of the different accesses to the phone line, PA1 connection of external terminals to card phones, in which the security of the telephone line is brought about by the network paying in real time the charge units emitted by the connection switch, connector for external terminals to public telephones installed in protected places, where the security of the connector is very limited. PA1 immunity to masking charge pulses by disturbances which could be generated by an ill-intentioned user (in the case where charging takes place by pulses emitted by the switch), PA1 checking the phone line connector by the public telephone and not by the external terminal, this function being necessary in all charge calculation modes, PA1 checking the dialling by the public phone in the case where there are restrictions with respect to calling certain numbers.
In the case of a dedicated interface between a public phone of a particular type and a terminal of a particular type, the security of the phone line is brought about "mechanically" by physical protection of all accesses to the phone line. This type of product is installed in direct view of the public telephone user. Moreover, this type of interface only functions with a public phone of a particular type and a terminal of a particular type. Reference can be made in exemplified manner to the device known as a "Point Phone" (registered trademark) and its interface for the "Minitel" (registered trademark), which makes it possible to obtain a "Publivideotex" (registered trademark). It is, for example, not possible to connect to such a product a portable microcomputer equipped with a modem. Another example relates to the Point Phone and a fax, which makes it possible to obtain a "Publifax" (registered trademark). In both cases, the interface between the Point Phone and the Minitel or fax is specific to each unit.
In the case of a connector of external terminals to card phones, the security of the phone line is brought about by real time payment of the charge units emitted by the connection switch. Between the card phone and the switch is inserted a device in cutoff. For each charge pulse emitted by the switch, the device interrogates the card phone to establish whether the charge has been received and debited from the card. In the case of an incorrect response, the device interrupts the communication. The dialogue between the card phone and the device takes place by an above voice link outside the telephony band. The security for the connector for the external terminal then takes place by an above voice dialogue. In this case the security is not supplied by the card phone, but by the network to which is connected this public telephone type.
In the case where the connector of external terminals is correctly fitted to the public telephone, security is limited. Therefore, the installation of this type of public telephone takes place in protected places, where the risks are minimized. Outside France, reference can be made to the making available to the user of a connector for an external terminal the public telephone developed by ATT and which is mainly installed at airports in the USA.
In order to significantly develop the possibility of connecting an external terminal to a public phone, it is necessary for the connector not to constitute a risk of non-payment for communications. Until now, only two possibilities, described hereinbefore, make it possible to bring about a general connection of external terminals to a connector.
In the case of a connector to card phones, it is necessary to have, in the connection switch areas, a device in order to follow in real time the payment for the communication. Even though this device offers all the necessary security, the connection of the card phone cannot take place at any random location, in the absence of the above voice device, and the card phone does not meet all the requirements made.
In the case where the connector of external terminals is connected directly to the public telephone, there is a high fraud risk. Therefore such a public telephone can only be installed when the monitoring thereof is permanently ensured by the operator.
In order to solve these different problems, an aim of the present invention is to offer users a connector for external terminals to public telephones ensuring a good immunity to attempts at fraud without requiring the aforementioned above voice device. The securities provided by the public telephone and not by the network.